Soil Temperature. NOT Air Temperature.Annual grassy weeds both annuals and perennials germinate at different times and under different environmental conditions. The three main annual grassy weeds that are prominent in turfgrass in the Spring are; crabgrass, foxtail and goosegrass. There are others, and these main three also may have different varieties within each species that may develop slightly differently. Other grassy weeds like Poa annua germinate in the fall.
- Crabgrass needs a soil temperature of 550F for about 5 days to start the germination process -
People like to use flowering plants to go by to determine when to have their pre-emergent down. This idea can give you a general time frame, but flower bud development is governed by air temperature and not soil temperature.
You WANT weed seeds to germinate
- Dithiopyr 2L, is capable of providing limited post-emergent control of crabgrass until the 2-3 leaf stage -